Look up and you might actually see your white blood cells. Here’s how.
Have you ever looked out the window on a plane, or stared at some clouds in the blue sky? If the answer is yes, then you may have seen hundreds of tiny, wiggly dots floating in your field of view. You may have also wondered if it’s normal to see such things. Well, we have good news for you; they are absolutely harmless and most people experience this phenomenon during their lifetime.
The first person to closely examine the phenomenon was a German ophthalmologist, Richard Scheerer, who first drew clinical attention to it in 1924. It is called the blue field entoptic phenomenon, or Scheerer’s phenomenon, and is characterized by the appearance of tiny, bright dots resembling small worms when looking at bright blue lights, such as the sky.
Scheerer named these dots blue-sky sprites. They seem to race back and forth in one’s vision, sometimes in repeated patterns. The short-lived “sprites” are only visible for a second or less, and travel small distances along seemingly twisted ways. Actually, the dots and their movements seem different in each of our eyes, and someone who’s looking with both of their eyes sees a mixture of them.
The blue field entoptic phenomenon is created by blood flowing through the capillaries that pass in front of the retina. More precisely, it’s the rare white blood cells inside the blood vessels that create the phenomenon. Although we have more red blood cells (they make up 90 percent of our blood after all), red blood cells absorb blue light while white blood cells don’t.
Imagine that these white blood cells create gaps in blood flow, because they are larger and flow through the capillaries less often that the red ones. When you look at the sky, for example, much of the blue light is absorbed by the red blood cells. White blood cells, on the other hand, let it through to the retina, which sends a signal to the brain about the increased brightness. Then, the brain and the eyes basically edit out the gaps created by the white cells, so they will look like tiny white lights, instead of dark shadows or spots.
A medical technique called the blue field entoptoscopy also relies on Scheerer’s phenomenon. It is used to estimate blood flow in the capillaries, which are located in front of the retinas, by showing the patient a blue light and a computer-generated picture of moving dots. Most people, however, see this phenomenon when looking at the sky, since it is the largest emitter of blue light.
So, experiencing the phenomenon is actually a good sign. It means that the flow of blood in your capillaries is healthy.
Sources: 1, 2, 3